A tensile screen for the windows of Castello Sforzesco: integrating anemometric, optical and mechanical tests in the early-stage design of bespoke textile hybrid structures in historical contexts

This paper presents an interdisciplinary methodology of implementing bespoke, low-impact, lightweight structures as additions to historical buildings with the aim of enhancing their performance in terms of visual, lighting and hygrothermal comfort. To do this, the study focuses on the renovation of Sala delle Asse, one of the most relevant rooms of Castello Sforzesco in Milan. The design task at hand is to produce self-standing vertical screens for the large-scale windows in the room, in order to reduce the amount of sunlight that reaches the frescos, as well as to block air drafts that bring humidity inside the room. The main challenge of the project proved to be the fragility of the direct context, since the screens must be sealed in the borders, but no perforations are allowed on the vaulted edges of the windows. Thus, a textile-hybrid structure is proposed as a solution, due to its self-standing principle that would not require drilling on the vault. The experimental campaign starts by performing preliminary anemometric measures on the room and by modelling the illuminance level based on the definition of the optical properties of the glazing surfaces. These analyses, combined with parametric simulations, gave results on the preferred position and optical requirements of the curtains. After a selection of materials with the right visual qualities was made, these textile materials went through further optical tests to check their compatibility with the comfort requirements. Design choices were updated with these test results and were followed by mechanical studies on the stretching properties of the unconventional knitted textile materials to define the project’s feasibility. This feedback loop of empirical data, in addition to a computational simulation of the structure’s behavior, was applied to the construction of a real-scale mock-up to test the bending active principle. The mock-up also gives experimental results on how to change the structure in further design steps. In conclusion, this paper proposes an integrated feedback process, started from the very early-stage of design, that is not commonly applied in the architectural practice. In addition, the paper argues that the presented methodology and design process can be potentially applied in further historical contexts.